Abdominal Aortic Aneurysm (AAA)

by Lit Sin Quek

Case Presentation

A 75-year-old obese man comes to the emergency department. He has history C.O.P.D., hypertension. He is a smoker and on regular follow-up with primary care. He describes sudden onset severe flank and back pain for past 2 hours. He denies any chest pain or dyspnea. He informs the physician about his chronic abdominal pain. His initial vital signs are HR 98 bpm, RR 24/min, BP 190/105 mmHg, T 36.9C. His examination revealed mild abdominal pain without rigidity or rebound tenderness. Bedside ultrasonography performed and the result is shown below.

What is your opinion about ultrasound image, size of aorta? What is the risk of rupture for the patient?

Introduction

Abdominal Aortic Aneurism (AAA) rupture is one of the serious problems which should be suspected in every hypotensive elderly with abdominal pain. This chapter’s learning objectives are;

Understand the epidemiology and pathogenesis of AAA

Appropriate diagnostic measures

Clinical Key Points

Recognize indications for referral

Abdominal Aortic Aneurysm (AAA)

AAA is defined by International Society for Cardiovascular Surgery and Society for Vascular Surgery as “a focal dilation (widening) of the abdominal aorta where the diameter is at least 50% larger than the expected normal diameter for that individual.” However, most clinicians will consider the diagnosis of an AAA if the diameter greater than 3 cm.

The leading causes of AAA are;

Atherosclerosis

Genetic predisposition (weakening vs. occlusion)

Connective tissue diseases

Marfan’s, Ehlers-Danlos

Infection (Syphilis, salmonella, others)

Epidemiology

There are many factors affecting AAA development. These factors are very critical to reaching the diagnosis and knowing those can help you during the history taking, even in the management of the patient. Factors Associated with AAA are as follows;

Old age: generally above 55 considered is a risky cut-off for AAA.

Gender: Men develop AAA 4-5 times more often than women

Ethnicity: White people develop AAA more frequently than other ethnicities

Cardiovascular risk factors and vascular bed affection: People with coronary artery disease and peripheral artery disease are more prone to have AAA.

Family history: A family history of AAA increases the risk of developing AAA. The risk of developing an AAA may reach 20% among brothers of a patient with a known AAA.

Smoking: It is a risk factor for many diseases. Number of years of smoking is related to high risk.

Diabetes mellitus: There is a negative association with diabetes mellitus and AAA.

Hypertension: It is a poor predictor for AAA development but important risk factor for expansion and rupture.

Lipid: There is no and weak correlation between risk for AAA and high serum triglyceride and cholesterol, respectively.

Emphysema: It is the strongest independent risk factor for rupture. Prevalence is 5% to 7% of people over the age of 65 in the United States. There is a 3:1 ratio of men to women. After age 65, the prevalence of 3 cm aneurysms in men increases by approximately 6% per decade.

Types of AAA

Saccular aneurysm – is an outpouching arising from one part of the aorta, has a neck, and does not involve the entire circumference of the aorta.

Fusiform aneurysm – is tubular in shape, involves the entire circumference of the localized aorta, and has no neck.

Pseudoaneurysm – dilatation is only at the outside layer of the aorta (tunica adventitia)

Mycotic aneurysm – a rare aneurysm caused by a fungal infection which may be associated with immunodeficiency, IV drug abuse, heart valve surgery.

Presentation

Abdominal/back pain, a pulsatile mass, and hypotension are known as the classic triad, but only seen 1/3 of the patients. So, you have to lower your threshold to be suspicious for cases showing epidemiologic warnings described above.

Critical Bedside Actions and General Approach

As described in many other chapters (e.g., Shock), the primary goal is the resuscitate any unstable patient. Therefore, airway, breathing, circulation should be evaluated immediately and resuscitative measures implemented. If the rupture is suspected, immediate surgical consultation and blood transfusion to the patient is a must. Do not delay the definitive treatment which is surgery.

Differential Diagnoses

Renal colic

Diverticulitis

GI bleeds

Myocardial infarction

Musculoskeletal back pain

The patients may have a variety of differential depending on their symptoms. The important clue to keep in mind is each of these specific diseases shows their specific symptoms, and as a rule of thumb, these symptoms may be indirectly mimicking AAA, especially elderly patients and patient who have risk factors.

History and Physical Examination Hints

Many of the patients are elderly. Because of their pain sensation affected by multiple comorbidities, AAA patients may not give clear history hints to physicians. Most of the times, symptoms are very subtle unless hypotension and shock situation in rupture. The patients showing epidemiologic risk factors should be questioned very carefully.

Physical examination of the patients should include relevant organ systems that patient having risk factors or symptoms. Specific attention should be given to understand instability.

Specific exam for AAA includes deep gentle palpation, above the umbilicus, left of midline, continuous over several heartbeats. Bleeding into retroperitoneum may create doughy abdomen. Hypotension also minimizes pulsations.

Some facts;

38% patients AAA initially detected by physical examination

62% found incidentally on imaging studies done for other indications

AAA detected by physical examination had lower BMI but there was no difference in AAA size

43 % of AAA detected on radiologic examination is palpable and should have been detected on physical examination.

23% AAA were not palpable on pre-operative physical examination, even when the diagnosis was known.

Obese patients had only 15% of AAA detected by physical examination, and only 33% were palpable.

Emergency Diagnostic Tests and Interpretation

Laboratory tests

The most important issue for these patients is bleeding. Therefore, type and cross-match blood is the most critical test. CBC, Urea/Creatinine, coagulation studies and urinalysis are other tests.

Abdominal aorta investigation with ultrasound. Tutorial in 3 minutes take a look.

CT Scan with contrast is a gold standard. It shows better demonstration extent and complications of an aneurysm, retroperitoneal blood because of rupture, and dissection. However, the patient instability affects the usage of this imaging modality.

MRI has no advantage over CT scan.

The angiogram is not preferred for diagnosis but good for pre-op “mapping.”

Abdominal X-Ray/KUB may incidentally show findings of AAA. AAA can be seen in 60-75% of cases in the x-ray with the calcification of aortic wall or paravertebral mass.
Cross-table lateral most helpful view and a negative study is not helpful.

Emergency Treatment Options

Medications

There are no specific medications for AAA patients. However, some patients may require blood pressure and arrhythmia management. In the unstable patients, intubation with rapid sequence intubation (RSI) protocol, fluid and blood replacement should be considered. Analgesics also an important part of the treatment.

Procedures

Any critically ill patient who diagnosed AAA (potentially rupture) should immediately be intubated and airway secured. This also prepares the patient for the operation theatre. Some patients may have no peripheral IV access because of their shock situation. These patients require an intraosseous line or central I.V placement. Although these resuscitative measures keep the patient alive and any ruptured patient should directly go to the operation theatre, you should also know some other red flags for the indications for repair of AAA.

Size more than 5.5 cm. However, 5.0 cm still used in common practice by many surgeons.

Symptoms such as abdominal or back pain, to groin in some cases or tenderness of AAA.

Risk of Rupture: Emphysema, smoking, hypertension increase likelihood of rupture. Regarding Powell et al.’s study aneurisms less than 5.5 cm in diameter has less than 1% of rupture in one year. Above 5.5 cm risk is between 9.4% to 32.4 (more than 7 cm).

Rupture (“Leak”) as we discussed above.

Other treatment options and management strategies should be thought in stable AAA patients such as;

Clinical Key Points – putting it all together

Abdominal aortic aneurysms are asymptomatic until they rupture, resulting in a mortality of 85 to 90%.

Urgent repair is the only definitive option for symptomatic patients.

Although the optimal group to be screened remains controversial,

Smoking men or women 65 to 75 years of age and 65 to 75 years of age non-smoking man should undergo screening and selective screening, respectively.

The threshold for elective repair is an aortic diameter of 5.5 cm in men and 5.0 cm in women, but this may vary with practices.

Endovascular repair results in lower perioperative morbidity and mortality than open repair, but the two methods are associated with similar mortality up to 10 years.

Patients treated with endovascular repair require long-term surveillance owing to a small risk of aneurysm sac reperfusion and late rupture.

Decisions regarding prophylactic repair — whether to pursue and what type of repair to perform must take into account anatomy (not all situations can undergo endovascular repair), operative risk, and patient preference.

Disposition Decisions

Admission criteria

All unstable patients should be transferred to operation theatre immediately.

Stable patients with high risk of rupture, if they are not going to operation theatre, they can be admited into ward or ICU depending on institution protocols.

Discharge criteria

Asymptomatic patients only patient group can be discharged if they do not have any risk factor for rupture. Patient with risk factors should be evaluated carefully. If they are decided to discharge, close follow-up in the clinic should be arranged. The outpatientclinic folow-up for other patients must also be arranged before their discharge from the emergency department. Instruction specific to AAA should be given to patients.

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